Leaf wetness within a lily canopy

Jacobs, A.F.G.; Heusinkveld, B.G.; Klok, Elisabeth J.

doi:10.1017/s1350482705001726

Cited by 8 publications

(5 citation statements)

References 20 publications

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“…The dew distribution was uneven within the shrub stands, changing along with the variations of meteorological conditions and leaf distribution and structure (Jacobs and Nieveen, 1995). Our results indicated that the accumulated dew formation amount was greater at 50 cm above the canopy while the dew duration was longer under the canopy, which were consistent with the results of Barradas and Glez-Medellín (1999) and Jacobs et al (2005). Jacobs et al (1994) indicated that the dew duration at different layers were the same within canopy in a corn field.…”

Section: Discussionsupporting

confidence: 88%

Effects of shrub species and microhabitats on dew formation in a revegetation-stabilized desert ecosystem in Shapotou, northern China

Pan

Wang

2014

J. Arid Land

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Dew is an important supplement water source in arid and semi-arid areas. In order to determine the dew formation on different kinds of soils associated with various shrub species and microhabitats, we performed measurement of accumulated dew formation amount and duration in October 2009 in a revegetation-stabilized arid desert ecosystem in Shapotou area, northern China. The results indicated that the accumulated dew formation amount was four times larger at open spaces as compared to under the canopy, and it was nearly twice as much under living Artemisia ordosica plants (L.A.) as compared to under living Caragana korshinskii plants (L.C.). The opposite characteristics were found for dew duration between different microhabitats. Dew amounts at different vertical heights around the shrub stands were in the order of 50 cm above the canopy>the canopy edge>under the canopy. Dew amount continued to increase after dawn, and the proportion of average accumulated dew amount after dawn accounting for the average maximum amount increased from above the canopy to under the canopy. Dew formation duration after sunrise accounted for more than 50% of the total formation duration during the day time. Contrary to the distribution characteristics of dew amount, dew duration after dawn and total dew formation duration during the day time were both highest under the canopy, followed by at the canopy edge and then at 50 cm above the canopy. The portion of dew duration after dawn accounting for the total dew duration during the day time increased from above the canopy to under the canopy. From these results, we may conclude that dew availability as a supplemental water resource for improving the microhabitats in water-limited arid ecosystems is position dependent especially for the plant microhabitats at different stands layers.

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Section: Discussionsupporting

confidence: 88%

Effects of shrub species and microhabitats on dew formation in a revegetation-stabilized desert ecosystem in Shapotou, northern China

Pan

Wang

2014

J. Arid Land

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“…In this study, the visual observation of dew onset was based on the first appearance of small droplets over the blades of turfgrass leaves and was not confused with guttation or exudation from cut blades. Under these conditions, flat plate sensors measured LWD with errors no greater than 30 min, similar to the results obtained by Pedro (1980) for corn and soybean leaves and by Lau et al (2000) for tomato leaflets, confirming the good capability of the flat plate sensor for measuring LWD, as also mentioned by Jacobs et al (2005) and Jacobs et al (2006).…”

Section: Methodssupporting

confidence: 88%

Leaf wetness duration measurement: comparison of cylindrical and flat plate sensors under different field conditons

2006

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In general, leaf wetness duration (LWD) is a key parameter influencing plant disease epidemiology, since it provides the free water required by pathogens to infect foliar tissue. LWD is used as an input in many disease warning systems, which help growers to decide the best time to spray their crops against diseases. Since there is no observation standard either for sensor or exposure, LWD measurement is often problematic. To assess the performance of electronic sensors, LWD measurements obtained with painted cylindrical and flat plate sensors were compared under different field conditions in Elora, Ontario, Canada, and in Piracicaba, São Paulo, Brazil. The sensors were tested in four different crop environments--mowed turfgrass, maize, soybean, and tomatoes--during the summer of 2003 and 2004 in Elora and during the winter of 2005 in Piracicaba. Flat plate sensors were deployed facing north and at 45 degrees to horizontal, and cylindrical sensors were deployed horizontally. At the turfgrass site, both sensors were installed 30 cm above the ground, while at the crop fields, the sensors were installed at the top and inside the canopy (except for maize, with a sensor only at the top). Considering the flat plate sensor as a reference (Sentelhas et al. Operational exposure of leaf wetness sensors. Agric For Meteorol 126:59-72, 2004a), the results in the more humid climate at Elora showed that the cylindrical sensor overestimated LWD by 1.1-4.2 h, depending on the crop and canopy position. The main cause of the overestimation was the accumulation of big water drops along the bottom of the cylindrical sensors, which required much more energy and, consequently, time to evaporate. The overall difference between sensors when evaporating wetness formed during the night was around 1.6 h. Cylindrical sensors also detected wetness earlier than did flat plates--around 0.6 h. Agreement between plate and cylinder sensors was much better in the drier climate at Piracicaba. These results allow us to caution that cylindrical sensors may overestimate wetness for operational LWD measurements in humid climates and that the effect of other protocols for angling or positioning this sensor should be investigated for different crops.

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“…maize, lilies, potatoes, etc. ), dew is best calculated with a more extended crop model (Jacobs et al 2005;2006b).…”

Section: Methodsmentioning

confidence: 99%

Towards Closing the Surface Energy Budget of a Mid-latitude Grassland

Jacobs

Heusinkveld

Holtslag

2007

Boundary-Layer Meteorol

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Observations for May and August, 2005, from a long-term grassland meteorological station situated in central Netherlands were used to evaluate the closure of the surface energy budget. We compute all possible enthalpy changes, such as the grass cover heat storage, dew water heat storage, air mass heat storage and the photosynthesis energy flux, over an averaging time interval. In addition, the soil heat flux was estimated using a harmonic analysis technique to obtain a more accurate assessment of the surface soil heat flux. By doing so, a closure of 96% was obtained. The harmonic analysis technique appears to improve closure by 9%, the photosynthesis for 3% and the rest of the storage terms for a 3% improvement of the energy budget closure. For calm nights (friction velocity u * < 0.1 m s −1 ) when the eddy covariance technique is unreliable for measurement of the vertical turbulent fluxes, the inclusion of a scheme that calculates dew fluxes improves the energy budget closure significantly.

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Leaf wetness within a lily canopy

Cited by 8 publications

References 20 publications

Effects of shrub species and microhabitats on dew formation in a revegetation-stabilized desert ecosystem in Shapotou, northern China

Effects of shrub species and microhabitats on dew formation in a revegetation-stabilized desert ecosystem in Shapotou, northern China

Leaf wetness duration measurement: comparison of cylindrical and flat plate sensors under different field conditons

Towards Closing the Surface Energy Budget of a Mid-latitude Grassland

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